This invention relates to a method and apparatus for recording electrocardiogram information. More particularly, the invention relates to an electrocardiogram information recording method and apparatus through which diagnosis is facilitated, such as diagnosis of ischemia.
Apparatus which continuously record an electrocardiogram for an extended period of time and then subsequently reproduce the recorded waveforms and discriminate a change in the waveforms have recently been developed for the purpose of discovering heart disease and gaining an accurate understanding of the condition of the disease.
These apparatus include some which allow the recording of electrocardiograms to be continued for 24 hours or longer.
In the prior art, these apparatus are adapted to compress the stored electrocardiogram signal and either continuously record or display the compressed electrocardiogram.
A method of recording electrocardiogram information for an extended period of time is disclosed in the specification of Japanese Patent Publication Kokoku Hei 2-63008.
This method involves recording the compressed electrocardiogram waveform on the right side of the recording paper in a portion occupying, say, two-thirds of the page, and recording the ST trend and heart rate (HR), which correspond to the recorded compressed electrocardiogram, on the portion of the recording paper on the left side. FIG. 11 illustrates an example of electrocardiogram information according to this method.
In accordance with this method, the ST trend and the HR are recorded so as to correspond to the compressed electrocardiogram. Therefore, if an abnormal point in the ST trend is followed up on the right side, the position of the abnormal electrocardiogram can be determined immediately. This is advantageous in that diagnosis is easy to perform.
Another method is disclosed in the specification of Japanese Patent Application Laid-Open No. 1-170440 (U.S. Pat. No. 4,896,677; GBP 2,214,309; West German Patent Application 3,843,714.7), although this is not necessarily a method solely for the extended recording of electrocardiograms.
This method involves superimposing electrocardiogram waveforms in synchronism with a prescribed characteristic point in the waveforms, and recording the superimposed waveforms while changing the displayed position in fixed amounts. FIG. 12 illustrates an example of electrocardiogram information according to this method. This method also makes it possible to readily visualize the deviation of ST so that ischemia can be diagnosed witch ease.
In the former method, however, the electrocardiogram waveforms themselves are compressed. As a consequence, the ST in one heartbeat cannot be visualized and the ST deviation cannot be seen. This hinders diagnosis of ischemia.
In the latter method, it is easy to diagnose ischemia since the deviation of the ST can readily be seen. However, the electrocardiogram itself cannot be observed, and therefore the position of an abnormal waveform cannot be determined.
Furthermore, if too many waveforms are superimposed, the ST deviation cannot be observed adequately, and it is required that the displayed position be changed when a certain number of waveforms have been superimposed. Consequently, when it is attempted to record electrocardiogram waveforms over a long period of time, a large recording area also is required. When it is attempted to reduce the recording area, the displayed waveforms must themselves be made small, but this has the effect of detracting from the merits of the method.